Removing White Pixels from Grayscale

[rich2005]

Maybe Gimp menu: Color -> Color-to-alpha
see: https://docs.gimp.org/en/plug-in-colortoalpha.html

White is the default to remove

edit: If the menu entry is greyed out your black/white image is in indexed/grey mode. Change to RGB Gimp menu: Image -> Mode -> RGB

sorry, I have absolutely no idea what PS..dotted circle option in the channel menu is

another edit: Since you are using a Mac and Gimp help might not be installed a useful resource is the Gimp help in PDF format see: http://gimp.linux.it/www/meta/